This invention relates to a process for the removal of aluminum chloride from a liquid solution thereof with the liquid metal chlorides resulting from the chlorination of titaniferous materials, and more particularly to an improved process of the removal of aluminum chloride which substantially eliminates loss of titanium tetrachloride, does not cause a substantial loss of ferric chloride from the liquid solution, and reduces the formation of HCl.
Titanium tetrachloride is produced commercially by chlorinating, under reducing conditions, titaniferous materials such as rutile or ilmenite, or other titaniumrich materials such as those obtained by beneficiating such ores. These raw materials, in addition to their titanium values, contain varying amounts of compounds of other metals, particularly iron and aluminum. Following the chlorination conversion of the titanium and other metals to their vaporous chlorides, the chlorides are recovered and condensed to the solid or liquid state depending upon the physical properties of the components and the recovery apparatus used. Usually a liquid sludge is obtained which is undesirably contaminated with dissolved impurities and undissolved solid material. The amount and type of chlorides present in the crude depends upon the exact composition of the titaniferous raw material chlorinated and the particular chlorination method utilized. However, the presence of aluminum chloride is to be expected in practically all cases where aluminum compounds are present in the raw materials or in the materials of construction of the apparatus, e.g., furnace bricks.
The art has recognized for some time that aluminum chloride is a highly corrosive component of the liquid metal chloride mixture. The aluminum chloride quickly and severely attacks metallic materials of construction in the processing apparatus and must either be quickly removed from the liquid or the apparatus must be specially lined with ceramic to prevent corrosion. An early attempt to overcome this problem is described in U.S. Pat. No. 2,600,881. This method is based on the discovery that water will form an insoluble noncorrosive compound of aluminum and thereby remove aluminum chloride from the other metal chlorides resulting from the chlorination reaction. It was recognized at the time of this teaching that the use of water in excess of a stoichiometric amount was undesirable because the water would react with the desired titanium tetrachloride to form titanium oxychlorides and cause loss of the titanium value of the titaniferous material. However, it has been found that in order to practice this method on a commercial scale at least 10% stoichiometric excess of water is necessary to insure complete aluminum chloride removal, because it is practically impossible to determine at a given point and time in the chlorination process what proportion of the metal chlorides exiting the reactor is in fact aluminum chloride, so slight excess of water is necessary to insure complete removal. This excess necessarily results in a corresponding loss in titanium values.
Another process which can be utilized to remove aluminum chloride from mixtures thereof with metal chlorides such as titanium tetrachloride is described in U.S. Pat. No. 3,066,010. This process involves contacting a gaseous mixture of metal chlorides containing aluminum chloride with a column of solid sodium chloride whereby the sodium chloride forms a solid complex with aluminum chloride and with any ferric chloride which may be present in the gaseous mixture. Although this process may be useful where it is desired to recover only the titanium tetrachloride from the gaseous mixture, in cases where ferric chloride is present in more than trace amounts, its removal will cause increased NaCl consumption and waste disposal problems and, furthermore, in many cases it is desired to retain ferric chloride for its economic value in areas such as water purification.
This invention provides for a process whereby the corrosive and undesirable aluminum chloride component of the mixture of liquid chlorides resulting from the chlorination of titaniferous materials can be completely removed and at the same time losses of titanium values are essentially eliminated, the potential valuable ferric chloride component of the mixture is retained, and HCl formation is reduced.